Network operators upgrading their networks from 2G/3G networks to 4G networks; want a network evolution solution which permits the leveraging of a portion of their installed baseband equipment. In some cases this means that multi-standard mixed mode radios are used to support efficient in-band combining to ease the service transition from 2G/3G equipment to 4G equipment. Emerging deployments of shared radio solutions for base stations operating on multiple standards face particular challenges in relation to operating on a common clock synchronization. Each standard usually run from its own clocking domain.
When the timing or synchronization reference is temporarily lost, a network's ability to maintain time and sync stability becomes critical to ensure continued optimal network performance. The time period that a network is able to maintain time and sync stability without a reference is called the holdover time.
Precise synchronization is especially critical in mobile networks for the successful call signal handoff and proper transmission between base stations, as well as for the transport of real-time services. If individual base stations drift outside the specified frequencies, mobile handoff performance decays, calls interfere, and calls cannot be made, resulting in high dropped-call rates and impaired data services. In the event that timing or synchronization reference is temporarily lost, a network's ability to maintain time or “holdover” becomes critical to ensure optimal network performance.
These synchronization issues are further dilapidating in shared baseband deployments since holdover requirements are not standard; they vary depending on the system type, complexity, and operator's requirements. In shared baseband deployments, two heterogeneous systems with independent synchronization inputs are expected to produce outputs which are synchronized to one another, typically so that they can be combined together without loss of data. Existing clock synchronization solutions provide limited holdover capabilities in the case where one or both of the systems lose their synchronization inputs, leading to the outputs becoming unsynchronized with each other.
For these reasons, traditional synchronization has limited capabilities in situations as described above.